Apple iPad charging modes analysis

The voltages on USB Data+ and Data– pins tell the iDevice how much current the USB port can supply. Let me sum up my research and all the available information on this topic.
[UPDATE: 2013]

USB pinout

Pin

Wire color

Description

1

Red

+5V

2

White

Data–

3

Green

Data+

4

Black

Ground

Apple charger specs

charger

voltage

max. current

max. power

USB 2.0

5V

500mA

2.5 Watt

iPhone charger(A1205, A1265, A1300)

5V

1A

5 Watt

iPad charger (A1357)

5.1V

2A

10 Watt

iPad 4 charger (A1401)

5.1V

2.4A

12 Watt

Charging modes

charging mode

Data–

Data+

actual currentdrawn by my iPhone4

actual currentdrawn by my original iPad

actual currentdrawn by my iPad3

500mA mode

2V

2V

100mA before handshake, 240mA, 350mA, 440mA on my desktop on different USBs (wtf?),550mA when connected to Macbook Air (incl. running from battery)

100mA before handshake, 480mA desktop PC, 920mA Macbook Air USB

100mA before handshake, 480mA desktop PC, 920mA Macbook Air USB

1A mode

2.75V

2V

520mA

800-900mA

950mA

2A mode

2V

2.75V

550mA

800-900mA

990mA

2.4A mode

2.66V

2.66V

?

?

?

The current drawn by a device remains constant even you unlock it and start some power hungry app.
You can notice that the currents seem a bit strange, but I’m looking into it. Maybe the devices need to be discharched completely – I’ll post an update later [april 2013]. EDIT: A completely discharched iPhone draws the same power.

Resistor configurations you can use in your project

Required Data+/– voltages can be set with a simple voltage divider circuit. You can select different resistors based on what you may have in stock. Data+ and Data– voltages probably don’t need to be precise but approximate. There’s some examples I found on the internet which should work:

resistor

500mA mode

1A mode

1A mode(genuine iPhone charger)

1A mode

2A mode

2A mode(genuine iPad charger)

2.4A mode (could work)

R1

75k

33k

75k

75k 1%

33k

43k2 1%

? 51k

R2

50k

22k

51k

49k9 1%

22k

49k9 1%

? 49k9

R3

75k

33k

39k

43k2 1%

33k

75k 1%

? 51k

R4

50k

47k

51k

49k9 1%

47k

49k9 1%

? 49k9

tested by me

–

ok

–

ok

ok

ok

–

device

500mA mode

1A mode

1A mode

1A mode

2A mode

2A mode

2.4A mode

iPhone 3GS

?

240mA?

?

?

?

?

?

iPhone 4

?

380mA

?

?

620mA

?

?

iPad 3

?

620mA

?

?

1.1A

?

?

Detailed table for 1A mode (33/22/33/47k set):

voltage

iPhone 4

iPad 3

≤ 4.3V

0mAnothing happens

80mAnothing happens

4.35V

0mAnothing happens

80mAnothing happenswhen voltage slowly drops from higher voltage, ‚Charging is not supported with this accessory.‘ alert screen pops up and 180mA is drawn